1. Field of the Invention
The present invention generally relates to electronic circuits and, more specifically, to so-called class-A amplifiers.
The present invention more specifically applies to audio or audio/video signal processing chains.
2. Discussion of the Related Art
In most audio or audio/video devices, signals received by an antenna, extracted from a tape, from a CD/DVD, etc. are, possibly after reprocessing, amplified to be exploited by a reproduction device (television, home cinema, etc.) equipped with a decoder. Most often, the signals transit from one device to another through SCART connectors while respecting levels set by standards or are, within a device, conveyed in compliance with the levels provided by such standards. For audio signals, a DOLBY standard sets the maximum deviation of audio signals to 2 volts RMS (approximately 5.6 volts peak to peak).
FIG. 1 is a simplified representation of a processing chain of the type to which the present invention applies as an example.
In this example, audio signals originating from an antenna 11, from a video tape 12, or from a digital system 13 are processed by one or several circuits 2 (AUDIO PROC.) before being amplified (block 3, AMP.) to be delivered to a SCART connector 4. The processings (demodulation, filtering, path separation, etc.) performed by circuits 2 are different according to the audio source but the signal(s) provided by circuit 2 need however all to be amplified to respect the DOLBY standard at the output. Other audio or video signals reach SCART connector 4 (arrows in dotted lines 15). These signals originate from parallel processing paths. For stereo signals in particular, left-hand and right-hand paths are amplified separately (while possibly sharing a same upstream circuit 2).
Processing function 2 and amplification function 3 are generally performed by circuits powered by different voltages V1 and V2 (V2 being greater than V1) and also made in different technologies, that is, with transistors capable of standing different voltages. In the example of the DOLBY standard, voltage V2 is on the order of 8 volts while the processing circuits are powered under a smaller voltage V1, for example, on the order of 3.3 volts. For simplification, reference will be made hereafter to high and low voltages, but these voltages still are of the same order of magnitude (one does not switch from a low voltage of a few volts to a high voltage of some hundred volts).
It would be desirable to be able to integrate the entire processing chain within the same integrated circuit. However, manufacturing this circuit with the technology adapted to the highest voltage adversely affects the bulk and generates unnecessary power consumption in the processing portion.
It would thus be desirable to make the amplifier in the low-voltage technology. But this poses the problem that low-voltage technology transistors cannot withstand the high voltage required to provide the amplified signal with the desired output voltage swing.